1. Field of the Invention
The present invention relates in general to a method for driving a plasma display panel (PDP). In particular, the present invention relates to a method for driving a PDP by providing sustain pulses with phase difference in a sustain period.
2. Description of the Related Art
PDP displays images by indicates of charges accumulated through electrode discharge. It is one of the most interesting plate display devices because, among other advantages, it can provide a large screen and display full-color images.
FIG. 1 is a cross-section of a conventional PDP structure comprising two glass substrates 1 and 7 with components formed thereon. Inert gas, such as Ne, Xe, is filled in the cavity between glass substrates 1 and 7. The components formed on the glass substrate 1 include sustain electrodes Xi and Xi+1 parallel to each other, and parallel scan electrodes Yi and Yi+1 deposed between sustain electrodes, a dielectric layer 3 and a protective film 5. The distance between Xi and Yi is shorter than that between Yi and Xi+1 and Xi and Yi are called an electrode pair (Xi, Yi). Sustain electrode Xi+1 and scan electrode Yi+1 form another electrode pair (Xi+1, Yi+1). The components formed on the glass substrate 7 include address electrodes A perpendicular to sustain electrodes and scan electrodes and the fluorescent material 9 formed thereon.
In addition, gas discharges D1 and D2 occur between electrodes pairs (Xi, Yi) and (Xi+1, Yi+1), accordingly. Thus, one electrode pair provides one display line. A cell is defined at the intersection of an electrode pair and a data electrode.
FIG. 2 is a block diagram illustrating a plasma display formed by the PDP cells shown in FIG. 1. As shown in the drawing, the PDP 100 comprises the scan electrodes Y1˜Yn, the sustain electrodes X1˜Xn and the address electrodes A1˜Am. In addition, the plasma display includes the control circuit 110, the Y scan drivers 112A and 112B, the X sustain driver 114 and the address driver 116. Y scan driver 112A generates waveforms in every period, and Y scan driver 112B generates scan pulses in address period only. The control circuit 110 generates control signals and image data signals for the drivers according to the external clock signal CLOCK, the image data signals DATA, the vertical synchronous signal VSYNC and the horizontal synchronous signal HSYNC, wherein the clock signal CLOCK represents the data transmittal clock, the image data signals DATA represents the image data, which is processed in control circuit 110 to be display data to fit the format for address driver, and the vertical synchronous signal VSYNC and the horizontal synchronous signal HSYNC respectively define the timing sequences of a frame and a scanning line. The display data is transmitted to the address driver 116 by the control circuit 110 and is written to each cell through the address electrodes A1˜Am while the Y scan driver 112B sequentially scans the scan electrodes Y1˜Yn in address period. The detailed operation is described below.
FIG. 3 is a diagram of a conventional PDP driving scheme to display a frame. As shown in the drawing, each frame is divided into eight sub-fields SF1˜SF8. The PDP field displays various gray scales for all of the scanning lines. Each sub-field includes three operating periods, that is, the reset period R1˜R8, the address period A1˜A8 and the sustain period S1˜S8. The reset period clears the residual charges of last sub-field and a certain amount of the wall charges remaining in each cell. The address period accumulates wall charges into the cell, which is to be displayed (i.e., turned ON), through address discharge. The sustain period sustains discharge for the cells which have accumulated charges through the address discharge. All of the PDP cells are processed at the same time during the reset period R1˜R8 and the sustain periods S1˜S8. The address operation is sequentially performed for scan electrode during the address period A1˜A8. Moreover, the display brightness is proportional to the length of the sustain period S1˜S8. In the example of FIG. 3, the length of the sustain periods S1˜S8 of the sub-fields SF1˜SF8 can be set at a ratio of 1:2:4:8:16:32:64:128 to display images in 256 gray scales.
FIG. 4 is a timing diagram of the driving waveform on the electrodes in a single sub-field of conventional process. The waveform on the address electrodes Ai is generated by the address driver 116, the waveform on the sustain electrodes X is generated by the X sustain driver 114, and the waveform on the scan electrodes Y1˜Yn is generated by the scan driver 112A and 112B. As shown in the drawing, each sub-field includes the reset period, the address period and the sustain period. The waveform of each period and resulting behavior are described in detail below.
At time point a (in FIG. 4) of the reset period, the voltage of the scan electrodes Y1˜Yn is set to 0 V, and a write pulse having a voltage of VS+VW is applied to the sustain electrode X, in which the voltage VS+VW exceeds the firing voltage between the sustain electrode X and the scan electrode Yi. Therefore, the global writing discharge W occurs between the sustain electrode X and the scan electrodes Y1˜Yn. This discharge process accumulates negative charges on the sustain electrode X and positive charges on the scan electrodes Y1˜Yn. The electric field produced by the accumulated negative charges and the positive charges cancels out the voltage drop between the sustain electrodes, thus the time of global writing discharge W is very short.
At time point b, the sustain electrode X is set to 0 V, and a sustain pulse 202 having a voltage of VS is applied to all of the scan electrodes Y1˜Yn, wherein the value of the voltage VS plus the voltage caused by the charges accumulated between the sustain electrodes must exceed the firing voltage between the scan electrodes Yi and the sustain electrode X. Thus, the total sustain discharge S occurs between the sustain electrode X and the scan electrodes Y1˜Yn. Unlike previous discharge process, this discharge process accumulates positive charges on the sustain electrode X and negative charges on the scan electrodes Yi.
At time point c, the scan electrodes Y1˜Yn are set to 0V, an erase pulse 203 having a voltage lower than VS is applied to the sustain electrode X. The erase pulse neutralizes a part of the charges. On the scan electrodes Y1˜Yn, required wall charges remain so that the write operation can proceed at a lower voltage in the subsequent address period.
In the address period, the voltage of the sustain electrode X and the scan electrodes Y1˜Yn are pulled up to VS at time point d. Scan pulse 204 is then sequentially applied to the scan electrodes Y1˜Yn from time point e, and an address pulse having a voltage of VA is applied to the address electrode A1˜Am at the same time to cause write discharge. Wall charge is written into the corresponding cell and the corresponding cell is turned ON.
After scanning all of the scan electrodes Y1˜Yn, the sustain period begins. The sustain electrode X and the scan electrode Yi are first set to 0 V. Sustain pulses 205 having the same voltage are then applied to the sustain electrode X and the scan electrodes Yi in an alternate way, i.e., at time point f and at time point g. Thus, the cell turned ON during the address period irradiates. It should be noted that the driving waveform described is only an example. The waveform varies in practice, but the same theory is applied.
FIGS. 5A˜5D show waveforms of the pulses provided to the scan electrode and the sustain electrode of different types during the sustain period. FIG. 5A shows the scan electrode and the sustain electrode driven by “positive & no gap” mode during the sustain period. FIG. 5B shows the scan electrode and the sustain electrode driven by “positive & gap” mode during the sustain period. FIG. 5C shows the scan electrode and the sustain electrode driven by “negative & no gap” mode during the sustain period. FIG. 5D shows the scan electrode and the sustain electrode driven by “negative & gap” mode during the sustain period. In the figures, pulse X indicates the voltage provided to the sustain electrode varying with time, pulse Y indicates the voltage provided to the scan electrode varying with time, and pulse (X-Y) indicates the voltage difference between the sustain electrode and the scan electrode varying with time. As shown in FIGS. 5A˜5D, the phase of the pulses provided to all sustain electrodes is the same, and the phase of the pulses provided to all scan electrodes is the same. In addition, the phase difference between the pulses respectively provided to the sustain electrode and the scan electrode is 180°.
However, PDP cells to be illuminated supplying the same voltage difference between the sustain electrode and the scan electrode induces gas discharge at the same time. Thus, the discharge current on the scan electrodes is great, especially when the numbers of the illuminated cell is large. In addition, the discharge current is greater when the percentage of Xe is increased. Thus, loading on the driving circuit of PDP is increased. In addition, the large discharge current generates notches on the waveform of the sustain pulse.
FIG. 6 shows the waveforms of the sustain pulses provided to the sustain electrode and the scan electrode, and the current on the scan electrode. In the figure, X(V) represents the voltage provided to the sustain electrode, Y(V) represents the voltage provided to the scan electrode, and Y(I) represents the current magnitude through the scan electrode. As shown in FIG. 6, currents 60 and 61 of the current waveform and notches 62 of the voltage waveform are generated on the scan electrode. Here, current 61 is called displacement current to charge or discharge the capacitive load of the panel in the sustain period.
However, the current 60 of the scan electrode cause notches 62 of the voltage generated on the scan electrode, and a driver having a higher current tolerance to drive the scan electrodes is required. In addition, the notches 62 of the voltage on the scan electrodes influence the gas discharge of PDP cells, causing cell extinction.